The present invention relates to a vacuum processing method and apparatus for subjecting an object to be processed, such as a semiconductor wafer, to vacuum processing.
When a semiconductor wafer (hereinafter abbreviated to xe2x80x9cwaferxe2x80x9d) is to be subjected to processing in a vacuum, helium (He) which is a heat-transfer gas flows into a space between the wafer and the mounting stand on which the wafer is mounted, heat is transferred by that helium between the wafer and the mounting stand, and thus the wafer is maintained at a predetermined temperature. The gap between the wafer and the mounting stand is extremely small, but it could become larger. If reaction products that have been deposited on the inner walls of the vacuum chamber during a process such as chemical vapor deposition (CVD) or etching should fall onto the mounting stand as particles, and then a wafer is placed on the mounting stand in that state, the particles could come between the surface of the mounting stand and the wafer, thus increasing the gap therebetween. In addition, an abnormality could occur in the electrostatic chuck within the mounting stand during the processing, which would also increase the gap between the wafer and the mounting stand. Similarly, if the position of the wafer on the wafer conveyor arm should slip, the wafer could be placed away from the helium gas ejection holes that open onto the surface of the mounting stand.
If there is any such vertical displacement of the wafer from the mounting stand or an error in the position of the wafer, the thermal transfer state between the wafer and the mounting stand will change, so that the temperature of the wafer could drift away from the predetermined temperature locally and thus variations could occur in the film formation or etching process. An apparatus such as that illustrated in FIG. 5 is used to detect any abnormal mounting state of the wafer beforehand, when the wafer has been placed on the mounting stand.
In FIG. 5, reference number 1 denotes a helium supply source, 12 denotes a mounting stand for a wafer W, and 11 denotes a gas supply path for supplying helium to the mounting stand 12. A valve 16 is provided in the gas supply path 11. Reference number 13 denotes a pressure controller that compares the gas pressure within the gas supply path 11, measured by a gas pressure gauge 14, with a set pressure, adjusts a pressure adjustment valve 15 in such a manner that the difference therebetween becomes zero, and thus controls the gas pressure within the gas supply path 11 so that it becomes equal to the set pressure.
In this case, the degree of opening of the pressure adjustment valve 15 when the wafer W is mounted correctly on the mounting stand 12 is previously stored as a normal value in a memory (not shown in the figure), a detection signal that corresponds to the degree of opening of the pressure adjustment valve is compared with a threshold value by a comparator 17, and, if the detection signal is greater than the threshold value, an abnormality detection signal is output and the operation is halted.
In the above described pressure adjustment valve 15, the relationship between the set pressure of helium and the degree of opening of the valve during normal operation is as shown by the solid line in FIG. 6 and that during abnormal operation is as shown by the broken line in FIG. 6. It is clear from this figure that the degree of opening of the valve varies far more than the set pressure of the gas but, on the other hand, the difference between the degree of opening of the valve during normal operation and the degree of opening of the valve during abnormal operation is small. This means that threshold value of the comparator 17 must be varied depending on the value of the set pressure. This is troublesome.
Moreover, if the original pressure of the helium is changed, as shown by way of example in FIG. 7, the relationship between the degree of opening of the valve and the set pressure during normal operation will also change. This makes it difficult to set the threshold value of the comparator 17 and there is a danger that even if detection is performed correctly during abnormal operation, the abnormality detection signal may be generated even during normal operation.
The present invention was devised in the light of the above described problems and has as an object thereof the provision of a technique that makes it possible to detect any leakage of a heat-transfer gas that is supplied into a gap between an object to be processed, such as a substrate, and the mounting stand, in a simple and accurate manner.
The present invention provides a vacuum processing method wherein a heat-transfer gas, which enables thermal transfer between an object to be processed and an electrostatic chuck, is supplied to the object to be processed that is mounted on top of the electrostatic chuck, and a predetermined processing is performed, wherein: the method comprises the steps of measuring a flowrate of the heat-transfer gas while the heat-transfer gas is being supplied; and determining whether an abnormality exists in the mounting state of the object to be processed, on the basis of the thus measured value.
A vacuum processing apparatus in accordance with the present invention comprises: a vacuum processing vessel for performing vacuum processing on an object to be processed; a mounting stand provided within the vacuum processing vessel and having a surface on which the object to be processed is mounted; heat-transfer gas ejection holes formed in the surface, to supply a heat-transfer gas into a gap formed between the object to be processed and the surface in order to maintain the object mounted on the surface of the mounting stand at a predetermined temperature; a gas supply path for supplying a heat-transfer gas to the gas ejection holes; a heat-transfer gas supply source connected to the gas supply path; a pressure adjustment device provided in the gas supply path, for adjusting the pressure of the heat-transfer gas within the gas supply path; a flowmeter provided in a downsteam side of the gas supply path from the pressure adjustment device, for measuring the flowrate of the heat-transfer gas towards the gas ejection holes; and a comparator for comparing the flowrate measured by the flowmeter against a threshold value, which corresponds to a flowrate measured by the flowmeter when the heat-transfer gas is leaking from between the object and the surface of the mounting stand in a normal state, and outputting a detection signal if the measured flowrate exceeds the threshold value.
This invention detects any leakage of the heat-transfer gas from between the wafer and the mounting stand that exceeds the threshold value that has been set beforehand, by monitoring the flowrate of the heat-transfer gas, which makes it possible to detect an abnormal gas leakage in a simple manner, even if the set pressure of the heat-transfer gas should change but there is no change in the set flowrate when an abnormal leakage state is generated. In addition, this invention enables early detection of mis-positioning of the object, on the surface of the mounting stand, warping of the object, or damage or the like, by detecting any gas leakage of a flowrate that exceeds the threshold value.
The apparatus of the present invention is preferably further provided with a pressing means for pressing the object to be processed onto the surface of the mounting stand, to ensure that there is no non-uniformity in the thermal transfer between the object and the mounting stand caused by warping of the object to be processed. In this case, the mounting stand is formed of a dielectric material and the pressing means is an electrostatic chuck comprising electrodes for electrostatic attraction that are provided adjacent to the surface of the mounting stand. In addition, if the pressure adjustment device is adjusted in such a manner that the gas in the gas supply path has a preset pressure that is selected from within the range of 1 to 20 Torr, the relationship between the gas pressure and the temperature of the object to be processed becomes linear, making it possible to control the temperature of the object to be processed to a high degree of accuracy.
The method of supplying the heat-transfer gas could be such that the gas is sealed between the object to be processed and the mounting stand by a configuration such that a mirror finish is formed on the surface of the mounting stand and the pressing means is set to press the object to be processed against the surface of the mounting stand with a pressure of at least 500 g/cm2. It should be noted, however, that an extremely small amount of gas will leak in practice, even with this sealing configuration. Examples of vacuum processing in accordance with this invention include film-formation and etching.